Negative electrode material comprising Mg (O) / C composite, negative electrode, lithium ion secondary battery, and method for producing Mg (O) / C composite

Abstract

The present invention provides a negative electrode material comprising a Mg (O) / C composite which is a carbide of Mg-MOF-74 (magnesium-based metal-organic framework-74) in which O is present or absent, a negative electrode comprising the negative electrode material, a lithium ion secondary battery comprising the negative electrode, and a method for manufacturing the Mg (O) / C composite.

Description

TECHNICAL FIELD

[0001] This application claims the priority benefit of Korean Patent Application No. 10-2024-0034255, filed on March 12, 2024, and Korean Patent Application No. 10-2025-0031510, filed on March 11, 2025, the disclosures of which are incorporated herein in their entirety by reference.

[0002] The present invention relates to a negative electrode material comprising a Mg(O) / C composite, a negative electrode comprising the same, a lithium ion secondary battery comprising the same, and a method of manufacturing the Mg(O) / C composite. BACKGROUND

[0003] Recently, lithium ion secondary batteries using a solid-state electrolyte as an electrolyte have been attracting attention. In order to improve the energy density of these lithium ion secondary batteries, it has been proposed to use lithium as a negative electrode active material. The capacity density (capacity per unit weight) of lithium is about 10 times that of graphite, which is a commonly used negative electrode active material. Therefore, when lithium is used as a negative electrode active material, thinning of the lithium ion secondary battery and an increase in power output can be achieved.

[0004] As a lithium ion secondary battery, for example, an anode-free lithium ion battery is known, which comprises a negative electrode active material layer containing a metal that forms an alloy with lithium and a carbon material.

[0005] The driving mechanism of the above-described anode-free lithium ion secondary battery is as follows: at the time of charging, metallic lithium is deposited on the negative electrode active layer and between the negative electrode active layer and the current collector, and at the time of discharging, the deposited metallic lithium is ionized and moves to the positive electrode.

[0006] However, when the above-described negative electrode active layer is used, lithium is deposited at the interface between the negative electrode active layer and the solid electrolyte layer, and dendrites are often formed in which lithium grows toward the positive electrode active layer through the pores of the solid electrolyte layer.

[0007] Therefore, there is a need to develop a negative electrode material capable of controlling such dendrite generation in order to improve the driving characteristics and life characteristics of the battery.

[0008] [Related Art Documents]

[0009] [Patent Documents]

[0010] Korean Patent Publication No. 10-2020-0052707 SUMMARY

[0011] [Technical Problem]

[0012] The present invention aims to provide a negative electrode material, a negative electrode, and a lithium ion secondary battery capable of improving the driving characteristics and life characteristics of the battery.

[0013] Furthermore, the present invention aims to provide an efficient method for preparing Mg(O) / C composites with excellent performance as anode materials.

[0014] [Technical Solution]

[0015] To achieve the above objectives, the present invention provides an anode material comprising a Mg(O) / C composite, wherein the composite is a carbide of Mg-MOF-74 (magnesium-based metal-organic framework-74), wherein O may or may not be present.

[0016] The present invention also provides a negative electrode comprising a negative electrode active material layer, the negative electrode active material layer comprising 35% to 60% by weight of the negative electrode material, 35% to 60% by weight of a conductive material and 3% to 15% by weight of a binder.

[0017] The present invention also provides a lithium-ion secondary battery, comprising: the negative electrode; the positive electrode; and an electrolyte disposed between the negative electrode and the positive electrode.

[0018] The present invention also provides a method for preparing Mg(O)C complex, comprising: a) A solution is prepared by dissolving the magnesium precursor and 2,5-dihydroxyterephthalic acid in a solvent; b) Adjust the pH of the solution to 9 to 11; c) Heat-treat the solution at 110°C to 140°C; d) The solid produced after drying and heat treatment was used to prepare Mg-MOF-74; and e) Carbonize the Mg-MOF-74 at 500°C to 1000°C.

[0019] [Beneficial Effects]

[0020] The negative electrode material, negative electrode, and lithium-ion secondary battery of the present invention contain a Mg(O) / C composite, which improves the driving characteristics and lifespan characteristics of the battery.

[0021] Furthermore, the preparation method of the Mg(O) / C composite of the present invention provides an efficient method for preparing a Mg(O) / C composite with excellent performance as a negative electrode material. Attached Figure Description

[0022] Figure 1 This is a schematic cross-sectional view of the structure of the lithium-ion secondary battery of the present invention.

[0023] Figure 2 These are scanning electron microscope (a) and energy dispersive X-ray spectroscopy (EDS) images (b) of the Mg(O) / C composite of the present invention.

[0024] Figure 3 This is a transmission electron microscope image of the Mg(O) / C composite of the present invention.

[0025] Figure 4 The figures are X-ray diffraction analysis results of the Mg(O) / C complexes prepared in the examples and comparative examples.

[0026] Figure 5 This is a graph showing the results of the measurement of the discharge capacity retention rate and charge / discharge efficiency of the lithium-ion secondary battery in Example 1 of Experimental Example 2.

[0027] Figure 6 This is a graph showing the confirmation results of the activity of the Mg(O) / C complex in Experimental Example 3.

[0028] Figure 7 This is a SEM image showing the morphology of the Mg(O) / C complex depending on pH adjustment during the preparation of the Mg(O) / C complex.

[0029] Figure 8 and Figure 9 This is a schematic cross-sectional view of the structure of the lithium-ion secondary battery of the present invention. Detailed Implementation

[0030] The invention will be described in more detail below to provide a better understanding of it.

[0031] The words and terms used in this specification and claims should not be construed as having their ordinary or dictionary meaning, but rather should be interpreted as having meanings and concepts consistent with the technical concept of the invention, based on the principle that the inventors may define the concepts of the terms in a manner they deem most appropriate to describe their invention. Furthermore, the terminology used herein is for describing exemplary examples only and is not intended to limit the invention. Unless the context clearly indicates otherwise, singular expressions include plural expressions.

[0032] When a component is described as "connected to another component, included in another component, or mounted on another component," it should be understood that the component may be directly connected to or mounted on another component, but there may also be additional intermediate components between them. On the other hand, when a component is described as "directly connected to or mounted on" another component, it should be understood that there may be no other components between them. Other expressions describing the relationship between components, such as "on top of" and "directly on top of," or "between" and "directly between," or "adjacent" and "directly adjacent," should be interpreted similarly.

[0033] As used herein, unless otherwise stated, the term "combination" includes mixtures, alloys, reaction products, etc.

[0034] The negative electrode material of the present invention comprises a Mg(O) / C complex, which is a carbide of Mg-MOF-74 (magnesium-based metal-organic framework-74). In the Mg(O) / C complex, O (oxygen) may or may not be present.

[0035] The Mg(O) / C complex has a structure that includes a mixture of crystalline and amorphous components.

[0036] The Mg(O) / C composite improves the dispersion between carbon and metal and ensures structural stability through the carbon matrix. It can also stabilize the interface between the solid electrolyte layer and the negative electrode active material layer during battery operation through the decomposition of MgO.

[0037] In the Mg(O) / C complex, the weight ratio of Mg to C can be from 1:0.5 to 10, more preferably from 1:1 to 4.

[0038] In the Mg(O) / C complex, the weight ratio of MgO to C can be from 1:0.25 to 5, more preferably from 1:0.5 to 2.

[0039] When Mg and MgO are included together in a Mg(O) / C complex, their weight ratio can be from 1:0.25 to 8, more preferably from 1:0.5 to 3.

[0040] The interatomic weight ratio or the interatomic and intermolecular weight ratio of the Mg(O) / C complex was determined by thermogravimetric analysis.

[0041] In the above, the particle size of the Mg(O) / C composite can be from 10 nm to 10 μm, preferably from 50 nm to 1 μm, and more preferably from 50 nm to 500 nm. The particle size can be measured using a particle size analyzer (manufacturer: Malvern).

[0042] Mg-MOF-74 (metal-organic framework-74 (magnesium)) can have, for example, the following structures.

[0043]

[0044] This invention relates to a negative electrode comprising a negative electrode active material layer, said negative electrode active material layer comprising 40 to 89 wt% of said negative electrode material, 10 to 50 wt% of a conductive material, and 1 to 10 wt% of a binder. The negative electrode material may comprise 100 wt% of a Mg(O) / C composite, or may comprise 80 to 99 wt% of a Mg(O) / C composite and 1 to 20 wt% of other materials, such as metals. Materials known in the art can be used as other materials, such as metals, but are not limited thereto.

[0045] The negative electrode active material layer may more preferably contain 60 to 89% by weight of negative electrode material, 10 to 35% by weight of conductive material and 1 to 7% by weight of binder.

[0046] The negative electrode may include a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer can also be called a protective layer in the sense of protecting the battery cell from dendrite formation.

[0047] The present invention also provides a lithium-ion secondary battery, comprising: the negative electrode; the positive electrode; and an electrolyte disposed between the negative electrode and the positive electrode.

[0048] The electrolyte may preferably include, but is not limited to, sulfide solid electrolytes.

[0049] Lithium-ion secondary batteries can be anodeless batteries.

[0050] This invention provides a method for preparing a Mg(O) / C complex, which includes the following steps: a) A solution is prepared by dissolving the magnesium precursor and 2,5-dihydroxyterephthalic acid in a solvent; b) Adjust the pH of the solution to 9 to 11; c) Heat-treat the solution at 110°C to 140°C; d) The solid produced after drying and heat treatment was used to prepare Mg-MOF-74; and e) Carbonize the Mg-MOF-74 at 500°C to 1000°C.

[0051] The magnesium precursor may be one or more selected from magnesium nitrate hexahydrate (Mg(NO3)2·6H2O), magnesium nitrate dihydrate (Mg(NO3)2·2H2O), magnesium nitrate (Mg(NO3)2), and magnesium hydroxide (Mg(OH)2).

[0052] Based on 100 parts by weight of magnesium contained in the magnesium precursor, the amount of 2,5-dihydroxyterephthalic acid can be 200 to 300 parts by weight. If the amount of 2,5-dihydroxyterephthalic acid is less than 200 parts by weight, the magnesium may not react completely; if the amount is greater than 300 parts by weight, the amount of unreacted material increases, which may lead to undesirable side reactions.

[0053] As a solvent, a solvent prepared by mixing dimethylformamide, ethanol and water in a volume ratio of 10 to 25:0.5 to 2:1, more preferably in a volume ratio of 15 to 20:0.7 to 1.5:1, can be used.

[0054] If dimethylformamide is mixed at a volume ratio less than 10, the size of Mg-MOF-74 may increase dramatically; if it is mixed at a volume ratio greater than 25, the structure of Mg-MOF-74 may not develop, which is undesirable. Furthermore, if ethanol is mixed at a weight ratio less than 0.5, the structure of Mg-MOF-74 may not develop, and if ethanol is mixed at a weight ratio greater than 2, the size of Mg-MOF-74 may increase dramatically, which is also undesirable.

[0055] In step b), the pH of the solution can be adjusted to 9 to 11, preferably 9 to 10.5, more preferably 9.5 to 10. A pH below 9 or above 11 is undesirable because Mg-MOF-74 is not synthesized.

[0056] pH can be adjusted, for example, by adding an alkaline substance such as NaOH.

[0057] Adjusting the pH leads to a reduction in the particle size of the Mg(O) / C composite, making it similar to non-graphite carbon materials (see...). Figure 7 ).

[0058] The heat treatment in step c) can be carried out at 110°C to 140°C, preferably at 120°C to 130°C. If the heat treatment is carried out below 110°C, the reaction may not occur, and if the heat treatment is carried out above 140°C, the complex may not form uniformly due to concentration changes caused by solvent evaporation, etc.

[0059] The heat treatment in step c) can be carried out for 18 to 30 hours, more preferably 23 to 30 hours.

[0060] If the heat treatment time is less than 18 hours, the reaction may not be fully completed; if it exceeds 30 hours, the size of Mg-MOF-74 will increase, which is undesirable.

[0061] Based on the total weight of the magnesium precursor and 2,5-dihydroxyterephthalic acid, the amount of solvent used can be 30 to 300 times by weight, preferably 50 to 200 times by weight, and more preferably 70 to 150 times by weight.

[0062] If the amount of solvent used is less than 30 times, the size of Mg-MOF-74 may increase; if it exceeds 300 times, it may be undesirable due to kinetic defects in the reaction.

[0063] In step d), a solid can be obtained by introducing the heat-treated reaction mixture into a solvent to obtain a precipitate. For example, this can be achieved by introducing the reaction mixture into methanol to produce a precipitate and then drying the precipitate. In this case, drying can be performed under vacuum.

[0064] The carbonization in step e) can be carried out at 500 to 1000°C, preferably 600 to 700°C. If the carbonization temperature is below 500°C or above 1000°C, the shape of the particles may be deformed, which is undesirable.

[0065] Carbonization can be carried out under an inert atmosphere.

[0066] Examples of the present invention will now be described in more detail.

[0067] <Composition of Lithium-ion Secondary Batteries>

[0068] Figure 8 This is a cross-sectional view illustrating a schematic construction of a lithium-ion secondary battery according to an example of the present invention.

[0069] An example of the present invention is a lithium-ion secondary battery (100), which is a so-called lithium-ion secondary battery that is charged and discharged by the movement of lithium ions between a positive electrode (10) and a negative electrode (20). Specifically, the lithium-ion secondary battery (100) includes a positive electrode (10), a negative electrode (20), and a solid electrolyte layer (30) disposed between the positive electrode (10) and the negative electrode (20), such as Figure 8 As shown.

[0070] (1) Positive electrode

[0071] like Figure 8 As shown, the positive electrode (10) includes a positive electrode current collector (12) and a positive electrode active material layer (14) arranged sequentially toward the negative electrode (20).

[0072] The positive current collector (12) can be a plate or a foil. The positive current collector (12) can be, for example, an alloy of one or more metals selected from indium, copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium and lithium.

[0073] The positive electrode active material layer (14) can reversibly adsorb and release lithium ions. The positive electrode active material layer (14) may include a positive electrode active material and a solid electrolyte.

[0074] The negative electrode active material can be a compound capable of inserting / removing lithium. Examples of compounds capable of inserting or removing lithium include: Li a A 1-b B' b D'2 (where 0.90≤a≤1.8, 0≤b≤0.5); Li a E1- b B' b O 2-c D' c (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); LiE 2-bB' b O 4-c D' c (where 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b B' c D' α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni 1-b- c Co b B' c O 2-α F' α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni 1-b-c Mn b B' c D' α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni 1-b-c Mn b B' c O 2-α F' α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni b E c G d O2 (where 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤0.1); Li a Ni b Co c Mn d G e O2 (where 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0.001≤e≤0.1); Li a NiG b O2 (where 0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2 (where 0.90≤a≤1.8, 0.001≤b≤0.1); Li a MnG b O2 (where 0.90≤a≤1.8, 0.001≤b≤0.1); Lia Mn2G b O4 (where 0.90≤a≤1.8, 0.001≤b≤0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiI'O2; LiNiVO4; Li (3-f) J2(PO4)3 (where 0≤f≤2); Li (3-f) Fe2(PO4)3 (where 0≤f≤2); LiFePO4; Li4Ti5O 12 (LTO); and any one of the above expressions.

[0075] In the above formula, A is Ni, Co, Mn or a combination thereof; B' is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements or a combination thereof; D' is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; F′ is F, S, P or any combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or any combination thereof; Q is Ti, Mo, Mn or any combination thereof; I' is Cr, V, Fe, Sc, Y or any combination thereof; and J is V, Cr, Mn, Co, Ni, Cu or any combination thereof.

[0076] Specific examples of positive electrode active materials may include lithium salts such as lithium cobalt oxide (hereinafter referred to as LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (hereinafter referred to as NCA), lithium nickel cobalt oxide (hereinafter referred to as NCM), lithium manganese oxide, lithium iron phosphate, and lithium sulfide. The positive electrode active material layer (14) may contain only one of these compounds as the positive electrode active material, or it may contain two or more of them.

[0077] In the aforementioned lithium salts, the positive electrode active material may comprise a lithium salt of a transition metal oxide having a layered rock salt structure. Here, "layered rock salt structure" refers to a structure in which oxygen atom layers and metal atom layers are arranged alternately and regularly in the direction of a cubic rock salt structure, such that each atom layer forms a two-dimensional plane. Furthermore, "cubic rock salt structure" refers to a sodium chloride-type structure as a crystal structure. For example, "cubic rock salt structure" refers to a structure in which face-centered cubic lattices formed by cations and anions are arranged at half the side length of the unit cell.

[0078] Lithium salts of transition metal oxides with this layered rock salt structure can be ternary lithium transition metal oxides, such as LiNi. x Co y Al z O2 (NCA) or LiNi x Co y Mn zO2 (NCM) (where 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1). The positive electrode active material layer (14) may include a ternary transition metal oxide lithium salt having such a layered rock salt structure as the positive electrode active material to improve the energy density and thermal stability of the lithium ion secondary battery (100).

[0079] Here, the shape of the positive electrode active material may be, for example, a particulate shape such as spherical or ellipsoidal. In addition, the particle size of the positive electrode active material is not particularly limited and may be within the range applicable to the positive electrode active material of a conventional lithium ion secondary battery. Further, the content of the positive electrode active material in the positive electrode active material layer (14) is not particularly limited and may be within the range applicable to the positive electrode of a conventional lithium ion secondary battery.

[0080] Of course, a compound having a coating on its surface, or a mixture of this compound and a compound having a coating, may also be used. The coating may include a coating element compound, such as an oxide, hydroxide, hydroxyoxide, oxycarbonate or basic carbonate of the coating element. The compounds constituting these coatings may be amorphous or crystalline. The coating elements contained in the coating may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof. The coating formation process may be carried out using any coating method (e.g., spraying, dipping, etc.) as long as the compound can be coated with these elements in a manner that does not adversely affect the properties of the positive electrode active material, which is well understood by those skilled in the art and will not be described in detail.

[0081] Specific examples of such coatings include, for example, Li2O-ZrO2.

[0082] The solid electrolyte contained in the positive electrode active material layer (14) may be the same as or different from the solid electrolyte contained in the solid electrolyte layer (30) described later.

[0083] In addition to the above-mentioned positive electrode active material and solid electrolyte, the positive electrode active material layer (14) may also appropriately contain additives such as a conductive agent, a binder, a filler, a dispersant or an ionic conductivity promoter.

[0084] The conductive agent may be, for example, graphite, carbon black, acetylene black, Ketjen black, carbon fiber or metal powder. The binder may also include, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride or polyethylene. As the filler, dispersant or ionic conductivity promoter, any known material conventionally used for lithium ion secondary battery electrodes may be used.

[0085] (2) Negative electrode

[0086] The negative electrode (20) may include a negative electrode current collector (22) and a negative electrode active material layer (24), which are arranged sequentially toward the positive electrode (10).

[0087] The negative electrode current collector (22) can be a plate or a foil. The negative electrode current collector (22) can include materials that do not react with lithium, i.e., do not form any alloys or compounds with lithium. The materials constituting the negative electrode current collector (22) can include, for example, copper, stainless steel, titanium, iron, cobalt, and nickel. The negative electrode current collector (22) can be composed of one of these metals, or it can be composed of an alloy or coating material of two or more metals.

[0088] In the initial state or after full discharge, the negative electrode active material layer (24) may not contain lithium in the negative electrode current collector (22), in the negative electrode active material layer (24), or between the negative electrode active material layer (24) and the solid electrolyte layer (30). As described later, when an example lithium-ion secondary battery (100) is overcharged, the active material contained in the negative electrode active material layer (24) may form an alloy or compound with the lithium ions migrating from the positive electrode (10), and as Figure 2 As shown, a metal layer (26) mainly composed of lithium can be formed (deposited) on the negative electrode (20). The metal layer (26) can be deposited between the negative electrode current collector (22) and the negative electrode active material layer (24), within the negative electrode active material layer (24), or in both regions. Between the negative electrode current collector layer (22) and the negative electrode active material layer (24), the metal layer (26) mainly composed of lithium can also be configured to be closer to the negative electrode current collector layer (22) rather than the negative electrode active material layer (24).

[0089] In addition to the Mg(O) / C composite described above, the negative electrode active material layer (24) may also include carbon material particles, metal particles, metal oxide particles, and a binder. By including the binder, the negative electrode active material layer (24) can be stabilized on the negative electrode current collector (22). The material constituting the binder can be, for example, a resin material such as styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride (PVDF), or polyethylene. The binder may include one or more resin materials selected from these types of resin materials.

[0090] The negative electrode active material layer (24) may also be appropriately equipped with additives used in conventional lithium-ion secondary batteries, such as fillers, dispersants, ion conductors, etc. Specific examples of additives are the same as those for the positive electrode described above.

[0091] The overall thickness of the negative electrode active material layer (24) is not particularly limited and can be from 1 μm to 100 μm, or from 10 μm to 60 μm. If the thickness of the negative electrode active material layer (24) is less than 1 μm, the performance of the lithium-ion secondary battery may not be sufficiently improved. If the thickness of the negative electrode active material layer (24) exceeds 100 μm, the resistance of the negative electrode active material layer (24) may be high, which may result in insufficient improvement of the performance of the lithium-ion secondary battery. By using the adhesive described above, the thickness of the negative electrode active material layer (24) can be easily ensured to be at an appropriate level.

[0092] Meanwhile, the negative electrode current collector (22) may further include a membrane, the membrane comprising a material capable of forming an alloy or compound with lithium, wherein the membrane may be disposed between the negative electrode current collector (22) and the negative electrode active material layer.

[0093] The negative electrode current collector (22) does not react with lithium metal, but this may make it difficult to deposit a smooth lithium metal layer on it. The above-mentioned film can also be used as a wetting layer to allow lithium metal to be deposited flatly on the negative electrode current collector (22).

[0094] Materials used in the membrane capable of forming alloys with lithium metal may include silicon, magnesium, aluminum, lead, silver, tin, or combinations thereof. Materials used in the membrane capable of forming compounds with lithium metal may include carbon, titanium sulfide, iron sulfide, or combinations thereof. The content of such materials used in the membrane may be a small amount within a range that does not affect the electrochemical properties and / or redox potential of the electrode. The membrane may be applied planarly to the negative electrode current collector (22) to prevent cracking during charging cycles of the lithium-ion secondary battery (100). The application of the membrane may be performed by physical deposition (e.g., evaporation or sputtering), chemical deposition, or electroplating.

[0095] The thickness of the membrane can range from 1 nm to 500 nm. For example, the thickness of the membrane can range from 2 nm to 400 nm. For example, the thickness of the membrane can range from 3 nm to 300 nm. For example, the thickness of the membrane can range from 4 nm to 200 nm. For example, the thickness of the membrane can range from 5 nm to 100 nm.

[0096] (3) Solid electrolyte layer

[0097] A solid electrolyte layer (30) is disposed between the positive electrode (10) and the negative electrode (20) (e.g., between the positive electrode active material layer (14) and the negative electrode active material layer (24)). The solid electrolyte layer (30) includes a solid electrolyte capable of enabling ion migration. The solid electrolyte layer (30) may include a sulfide-based solid electrolyte.

[0098] Sulfide solid electrolytes can include Li₂S-P₂S₅, Li₂S-P₂S₅-LiX (where X is a halogen element), Li₂S-P₂S₅-Li₂O, Li₂S-P₂S₅-Li₂O-LiI, Li₂S-SiS₂, Li₂S-SiS₂-LiI, Li₂S-SiS₂-LiBr, Li₂S-SiS₂-LiCl, Li₂S-SiS₂-B₂S₃-LiI, Li₂S-SiS₂-P₂S₅-LiI, Li₂S-B₂S₃, and Li₂S-P₂S₅-Z. m S n (where m and n are positive numbers, and Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (Where p and q are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, or In) or any combination thereof. The solid electrolyte may include one material selected from these sulfide-based solid electrolyte materials, or may include two or more materials selected from them.

[0099] Sulfide solid electrolytes may include solid electrolytes represented by the following formula 1: <Formula 1> Li x M' y PS z A w Where x, y, z, and w are independently 0 to 6; M' is at least one of As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta; and A is at least one of F, Cl, Br or I.

[0100] As a solid electrolyte, sulfide-based solid electrolyte materials containing sulfur (S), phosphorus (P), and lithium (Li) as components can be used. For example, materials containing Li₂S-P₂S₅ can be used. When using materials containing Li₂S-P₂S₅ as sulfide-based solid electrolyte materials, the mixing molar ratio of Li₂S and P₂S₅ can be selected in the range of, for example, 50:50 to 90:10.

[0101] Furthermore, solid electrolytes can be amorphous or crystalline phases. They can also exist in a mixed state of amorphous and crystalline phases.

[0102] The solid electrolyte layer (30) may further comprise an adhesive. Examples of adhesive materials may include resins such as styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polyacrylic acid, etc. The adhesive material may be the same as or different from the adhesives constituting the positive electrode active material layer (14) and the negative electrode active material layer (24).

[0103] (4) Composition of lithium-ion secondary batteries

[0104] like Figure 8 As shown, the lithium-ion secondary battery (100) of the present invention can be a lithium-ion secondary battery (100) comprising a positive electrode (10), a solid electrolyte layer (30) and a negative electrode (20) in sequence.

[0105] <Preparation Methods of Lithium-ion Secondary Batteries>

[0106] Next, the manufacturing method of the lithium-ion secondary battery (100) will be described. An example lithium-ion secondary battery (100) can be obtained by separately manufacturing a positive electrode (10), a negative electrode (20) and a solid electrolyte layer (30), and then stacking the layers.

[0107] (1) Manufacturing process of the positive electrode

[0108] An example of the manufacturing process for the positive electrode is as follows. First, the materials constituting the positive electrode active material layer (14) (positive electrode active material, binder, etc.) are added to a non-polar solvent to form a slurry (or paste). The resulting slurry is then coated onto a prepared positive electrode current collector (12). It is dried to obtain a laminate. Then, the obtained laminate is pressurized, for example, using hydrostatic pressure, to obtain the positive electrode (10). In this case, the pressurization process can be omitted.

[0109] (2) Manufacturing process of negative electrode

[0110] An example of the manufacturing process of the negative electrode is as follows. First, the material constituting the negative electrode active material layer (24) is added to a polar or non-polar solvent to prepare a slurry (or paste). Then, the obtained slurry is coated onto the prepared negative electrode current collector (22) to form the negative electrode active material layer.

[0111] If the negative electrode active material layer also includes one or more additional layers, the additional layers can be stacked in the same manner as described above.

[0112] Then, for example, hydrostatic pressure is used to pressurize the laminate obtained by the above method to manufacture the negative electrode (20). Alternatively, the pressurization step can be omitted. In addition, there is no particular limitation on the method of coating the slurry onto the negative electrode current collector (22), and examples include screen printing, metal mask printing, electrostatic coating, dip coating, spraying, roller coating, doctor blade coating, gravure coating, etc.

[0113] The above describes a method for forming a two-layer negative electrode active material layer. However, even when forming an additional layer, the negative electrode can be prepared by preparing a slurry for forming each layer and stacking the layers sequentially in the stacking order using the method described above.

[0114] (3) Manufacturing process of solid electrolyte layer

[0115] The solid electrolyte layer (30) can be made of a solid electrolyte, including, for example, sulfide-based solid electrolyte materials.

[0116] First, raw materials (e.g., Li₂S, P₂S₅, etc.) are processed by melt quenching or mechanical grinding to obtain sulfide-based solid electrolyte materials. For example, in the case of using melt quenching, sulfide-based solid electrolyte materials can be prepared by mixing predetermined amounts of raw materials, granulating them, reacting them in a vacuum at a predetermined reaction temperature, and then quenching them. Furthermore, the reaction temperature of the mixture of Li₂S and P₂S₅ can be from 400°C to 1000°C, for example, 800°C to 900°C. In addition, the reaction time can be from 0.1 to 12 hours, for example, 1 to 12 hours. Furthermore, the quenching temperature of the reaction mixture can be below 10°C, for example, below 0°C, and the quenching rate is typically from 1°C / second to 10000°C / second, for example, 1°C / second to 1000°C / second.

[0117] Alternatively, in the case of mechanical grinding, sulfide-based solid electrolyte materials can be prepared by stirring and reacting the raw materials using a ball mill or similar equipment. Furthermore, there are no particular limitations on the stirring speed and time in mechanical grinding, but faster stirring speeds result in more rapid production of sulfide-based solid electrolyte materials; and longer stirring times lead to a higher conversion rate of the raw materials to sulfide-based solid electrolyte materials.

[0118] The resulting mixed raw materials (sulfide-based solid electrolyte materials) are then heat-treated at a predetermined temperature and subsequently pulverized to produce granular solid electrolytes. When a solid electrolyte has a glass transition point, it can undergo a phase transition from an amorphous to a crystalline state through heat treatment.

[0119] Next, a film can be formed using known techniques such as aerosol deposition, cold spraying, or sputtering to form a solid electrolyte layer (30) from the solid electrolyte obtained by the above method. Alternatively, the solid electrolyte layer (30) can be prepared by pressurizing solid electrolyte particles. Furthermore, the solid electrolyte layer (30) can be prepared by mixing the solid electrolyte with a solvent and a binder, coating, drying, and pressurizing.

[0120] (4) Stacking process

[0121] An example of a lithium-ion secondary battery (100) can be obtained by placing a solid electrolyte layer (30) between a positive electrode (10) and a negative electrode (20) and pressurizing it using, for example, hydrostatic pressure.

[0122] The lithium-ion secondary battery (100) of the present invention uses end plates and does not require the application of high external pressure. Even when the external pressure applied to the positive electrode (10), negative electrode (20) and solid electrolyte layer (30) is less than 1 MPa, it can provide improved discharge capacity during use.

[0123] <Charging Methods for Lithium-ion Secondary Batteries>

[0124] Next, the charging method of the lithium-ion secondary battery (100) will be explained.

[0125] One example of a method for charging a lithium-ion secondary battery (100) may include charging the battery beyond the charging capacity of the negative electrode active material layer (24), i.e., overcharging.

[0126] In the early stages of charging, lithium can be adsorbed within the negative electrode active material layer (24). When the battery is charged beyond the charging capacity of the negative electrode active material layer (24), lithium can be deposited on the back side of the negative electrode active material layer (24), i.e., between the negative electrode current collector (22) and the negative electrode active material layer (24), such as... Figure 9 As shown, the deposited lithium can form a metal layer (26) that is not present during manufacturing. During discharge, lithium in the negative electrode active material layer (24) and the metal layer (26) can be ionized and migrate to the positive electrode (10) side. Therefore, lithium can be used as the negative electrode active material in the lithium-ion secondary battery (100) of the present invention. In addition, since the negative electrode active material layer (24) covers the metal layer (26), it can function as a protective layer for the metal layer (26) and suppress the deposition and growth of dendritic lithium metal. In this way, short circuits and capacity degradation of the lithium-ion secondary battery (100) can be suppressed, and the characteristics of the lithium-ion secondary battery (100) can be improved. Furthermore, according to one example, the metal layer (26) is not pre-formed, which can reduce the manufacturing cost of the lithium-ion secondary battery (100).

[0127] In addition, the metal layer (26) is not limited to Figure 9 The metal layer shown, formed between the negative electrode current collector (22) and the negative electrode active material layer (24), can also be formed inside the negative electrode active material layer (24). In addition, the metal layer (26) can be formed between the negative electrode current collector (22) and the negative electrode active material layer (24) and inside the negative electrode active material layer (24).

[0128] The lithium-ion secondary battery (100) of the present invention can be configured as a single cell having a positive electrode / separator / negative electrode structure, a dual cell having a positive electrode / separator / negative electrode / separator / positive electrode structure, or a stacked cell structure with repeated single cell configurations.

[0129] The lithium-ion secondary battery (100) of the present invention is not particularly limited in shape, and may include, for example, coin-shaped, button-shaped, sheet-shaped, stacked, cylindrical, flat, or prismatic shapes. It can also be applied to large batteries used in electric vehicles. For example, the lithium-ion secondary battery (100) can also be used in hybrid electric vehicles, such as plug-in hybrid electric vehicles (PHEVs). It can also be used in applications requiring large amounts of energy storage. For example, it can be used in electric bicycles or power tools.

[0130] Example

[0131] The present invention will be described in detail below through embodiments. However, the embodiments of the present invention can be modified in many other ways, and the scope of the present invention should not be construed as limited to the embodiments described below. The embodiments of the present invention are provided to more fully illustrate the invention to those skilled in the art.

[0132] Example 1: Manufacturing of Lithium-ion Secondary Batteries

[0133] (1) Preparation of Mg-MOF-74

[0134] 1.4 g of magnesium nitrate hexahydrate (Mg(NO3)2·6H2O) and 0.337 g of 2,5-dihydroxyterephthalic acid were dissolved in 153 ml of a solution of dimethylformamide, ethanol, and water in a volume ratio of 15:1:1. Subsequently, 10% NaOH aqueous solution was slowly added to adjust the pH to 9.5, and the mixture was then mixed for 1 hour and sealed. The mixture was then heat-treated in a calcining furnace at 125 °C for 26 hours. The reaction mixture was then added to methanol, and the resulting precipitate was dried under vacuum to obtain Mg-MOF-74.

[0135] (2) Preparation of Mg(O) / C complex

[0136] The Mg-MOF-74 obtained in step (1) was heat-treated at 600°C for 6 hours under an argon atmosphere to prepare a Mg(O) / C complex. The particle size of the prepared Mg(O) / C complex was 50 nm. Furthermore, the weight ratio of Mg to C in the Mg(O) / C complex was 1:1.5.

[0137] (3) Preparation of negative electrode

[0138] An adhesive solution was prepared by mixing polyvinylidene fluoride (PVDF) with n-methylpyrrolidone (NMP) solvent. Next, the Mg(O) / C composite prepared in Example 1 was mixed with carbon black at a 1:1 weight ratio and then mixed with the adhesive solution. At this point, PVDF was mixed at 7 parts by weight relative to a total of 100 parts by weight of Mg(O) / C composite and carbon black.

[0139] The mixture was stirred using a Thinky mixer to control the viscosity. After adjusting the viscosity, 2 mm zirconia balls were added and the mixture was stirred again using the same mixer to prepare a slurry.

[0140] The slurry is coated onto a stainless steel (SUS) foil and vacuum dried at 100°C to produce a negative electrode with a 10 μm thick layer of negative electrode active material.

[0141] (4) Manufacturing of the positive electrode

[0142] LiNi as a hybrid positive electrode active material 0.8 Co 0.1 Mn 0.1 The active material consists of O2 (NCM), Li6PS5Cl as a sulfide-germanium ore-type solid electrolyte, carbon nanofibers (CNF) as a conductive material, and polytetrafluoroethylene (PTFE) as a binder. The weight ratio of the positive electrode active material, solid electrolyte, conductive material, and binder is 80:18:1:1. After mixing the mixture in a mixer, a dried sheet is prepared using a roller press. The dried sheet is then bonded to an aluminum current collector to prepare a positive electrode with a 150 μm thick positive electrode layer.

[0143] (5) Manufacturing of solid electrolytes

[0144] Butyl butyrate (NBB) was added as a binder solution to the silver sulfide germanite-type solid electrolyte Li6PS5Cl, and the mixture was stirred using a Thinky mixer to control the viscosity. After adjusting the viscosity, 2 mm zirconia balls were added and the mixture was stirred again using the same mixer to prepare a slurry. The slurry was cast onto a PET release film and dried at room temperature to prepare the solid electrolyte.

[0145] (6) Manufacturing of lithium-ion secondary batteries

[0146] Cut the prepared positive electrode into 4 cm pieces. 2 The solid electrolyte prepared above was cut into 5.76 cm square pieces. 2 The prepared negative electrode is cut into square pieces of 4.84 cm. 2 Square shapes are stacked to prepare lithium-ion secondary batteries.

[0147] Example 2: Manufacturing of Lithium-ion Secondary Batteries

[0148] The lithium-ion secondary battery was prepared in the same manner as in Example 1, except that in the step “(1) Preparation of Mg-MOF-74” in Example 1, the pH was adjusted to 10.

[0149] The prepared Mg(O) / C composite had a particle size of 50 nm and was used in the fabrication of the negative electrode.

[0150] Comparative Example 1: Manufacturing of Lithium-ion Secondary Batteries

[0151] The lithium-ion secondary battery was prepared in the same manner as in Example 1, except that in the step “(1) Preparation of Mg-MOF-74” in Example 1, the pH was adjusted to 8.5.

[0152] The prepared Mg(O) / C composite had a particle size of 5 μm and was used in the manufacture of the negative electrode.

[0153] Comparative Example 2: Manufacturing of Lithium-ion Secondary Batteries

[0154] The lithium-ion secondary battery was prepared in the same manner as in Comparative Example 1, except that in the step “(1) Preparation of Mg-MOF-74” in Example 1, dimethylformamide, ethanol and water were mixed in a volume ratio of 38:1:1 instead of 15:1:1.

[0155] The prepared Mg(O) / C composite had a particle size of 15 μm and was used in the manufacture of the negative electrode.

[0156] Comparative Example 3: Manufacturing of Lithium-ion Secondary Batteries

[0157] The lithium-ion secondary battery was prepared in the same manner as in Comparative Example 1, except that in the step “(1) Preparation of Mg-MOF-74” in Example 1, 0.674 g of 2,5-dihydroxyterephthalic acid was used instead of 0.337 g of 2,5-dihydroxyterephthalic acid.

[0158] The prepared Mg(O) / C composite had a particle size of 20 μm and was used in the manufacture of the negative electrode.

[0159] Comparative Example 4: Manufacturing of Lithium-ion Secondary Batteries

[0160] The lithium-ion secondary battery was prepared in the same manner as in Comparative Example 1, except that in the step “(1) Preparation of Mg-MOF-74” of Example 1, the battery was heat-treated in a calcining furnace for 16 hours instead of 26 hours.

[0161] The prepared Mg(O) / C composite had a particle size of 10 μm and was used in the manufacture of the negative electrode.

[0162] Comparative Example 5: Manufacturing of Lithium-ion Secondary Batteries

[0163] The lithium-ion secondary battery was prepared in the same manner as in Comparative Example 1, except that in the step “(1) Preparation of Mg-MOF-74” in Example 1, 460 mL of a solution of dimethylformamide, ethanol and water in a volume ratio of 15:1:1 was used instead of 153 mL of the solution.

[0164] The prepared Mg(O) / C composite had a particle size of 2 μm and was used in the manufacture of the negative electrode.

[0165] Comparative Example 6: Manufacturing of Lithium-ion Secondary Batteries

[0166] The lithium-ion secondary battery was prepared in the same manner as in Comparative Example 1, except that in the step “(3) Preparation of negative electrode” of Example 1, instead of using a mixture of Mg(O) / C composite and carbon black in a weight ratio of 1:1, twice the amount of carbon black was used without using Mg(O) / C composite.

[0167] Experimental Example 1: Evaluation of the discharge capacity of lithium-ion secondary batteries

[0168] The lithium-ion secondary batteries prepared in Examples 1, 2, and Comparative Examples 1 to 6 were operated at 60°C in a voltage range of 2.5 V to 4.3 V, and their discharge capacity was evaluated.

[0169] [Table 1]

[0170] Experimental Example 2: Evaluation of Discharge Capacity Retention and Charge / Discharge Efficiency of Lithium-ion Secondary Batteries

[0171] The discharge capacity retention and charge / discharge efficiency of the secondary battery prepared in Example 1 were determined by performing CC charging and CC discharging at 0.2C within a voltage range of 2.5V to 4.3V at 60°C. The results are shown below. Figure 5 .

[0172] Experimental Example 3: Verifying the activity of Mg(O) / C composites that differ from non-graphite carbon-based active materials

[0173] The Mg(O) / C composite prepared in Example 1 was used to construct the negative electrode, and lithium metal was used as the counter electrode. The mixture was then pressed into a sheet to prepare a half-cell. The activity of the Mg(O) / C composite was measured by subjecting the half-cell to CC charging and CC discharging at a current of 0.1C within a voltage range of 0 V to 1.5 V. The results of the activity verification are shown in... Figure 6 In the middle. For example Figure 6 As shown, the Mg(O) / C composite of the present invention exhibits activity different from that of non-graphite-based active materials.

[0174] [Figure Labels]

[0175] 1: Negative electrode current collector

[0176] 2: Negative electrode active material layer

[0177] 3: Solid electrolyte layer

[0178] 4: Positive electrode active material layer

[0179] 5: Positive current collector

[0180] 6: Mg(O) / C complex

[0181] 7: Mg or MgO nanoparticles

[0182] 8: Carbon structure

Claims

1. A negative electrode material comprising a Mg(O) / C complex, wherein the Mg(O) / C complex is a carbide of Mg-MOF-74 (magnesium-based metal-organic framework-74), wherein O may or may not be present.

2. The negative electrode material as described in claim 1, wherein, The weight ratio of Mg to C in the Mg(O) / C complex is from 1:0.5 to 10.

3. The negative electrode material as described in claim 1, wherein, The weight ratio of MgO to C in the Mg(O) / C composite is 1:0.25 to 5.

4. The negative electrode material as described in claim 3, wherein, When Mg and MgO are included together in the Mg(O) / C complex, their weight ratio is 1:0.25 to 8.

5. A negative electrode comprising a negative electrode active material layer, said negative electrode active material layer comprising 35% to 60% by weight of the negative electrode material of claim 1, 35% to 60% by weight of a conductive material and 3% to 15% by weight of a binder.

6. A lithium-ion secondary battery, comprising: The negative electrode and positive electrode as described in claim 5; and the electrolyte disposed between the negative electrode and the positive electrode.

7. The lithium-ion secondary battery as described in claim 6, wherein, The electrolyte includes sulfide solid electrolytes.

8. The lithium-ion secondary battery as described in claim 7, wherein, The lithium-ion secondary battery is an anode-free battery.

9. A method for preparing a Mg(O) / C complex, comprising: a) A solution is prepared by dissolving the magnesium precursor and 2,5-dihydroxyterephthalic acid in a solvent; b) Adjust the pH of the solution to 9 to 11; c) Heat-treat the solution at 110°C to 140°C; d) Dry the solid produced after the heat treatment to prepare Mg-MOF-74; and e) Carbonize the Mg-MOF-74 at 500°C to 1000°C.

10. The method for preparing the Mg(O) / C complex as described in claim 9, wherein, The magnesium precursor is selected from one or more of the group consisting of magnesium nitrate hexahydrate (Mg(NO3)2·6H2O), magnesium nitrate dihydrate (Mg(NO3)2·2H2O), magnesium nitrate (Mg(NO3)2), and magnesium hydroxide (Mg(OH)2).

11. The method for preparing the Mg(O) / C complex as described in claim 9, wherein, Based on 100 parts by weight of magnesium contained in the magnesium precursor, the amount of 2,5-dihydroxyterephthalic acid is 200 to 300 parts by weight.

12. The method for preparing the Mg(O) / C complex as described in claim 9, wherein, The solvent is a mixture of dimethylformamide, ethanol and water in a weight ratio of (10 to 25):(0.5 to 2):

1.

13. The method for preparing the Mg(O) / C complex as described in claim 9, wherein, The heat treatment in step c) is carried out for 18 to 30 hours.

14. The method for preparing Mg(O) / C complex as described in claim 12, wherein, The amount of solvent used is 30 to 300 times the weight of the total weight of the magnesium precursor and 2,5-dihydroxyterephthalic acid.

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